The subunit composition and assembly mechanisms of ferritin from various sources will be examined. Aspects of primary structure, conformation and molecular interactions will be probed by physical and chemical means, in an effort to gain insight into the mechanisms by which the protein mediates iron deposition and mobilization in mammalian cells. Aspects of microheterogeneity of different ferritins will be related to subunit heterogeneity. The two classes of subunits found in most ferritins (H and L types) will be purified to homogeneity, and reassembled to form discrete apoferritin moieties. Iron loading functions, and other properties of these apoferritins will be studied. Specific antisera (H or L) will be prepared to determine levels of different species of ferritin in tissues and sera. Biosynthesis studies and mechanisms of differential regulation of the two subunits in response to iron will be investigated in detail.